Soil-nailing is a process of construction which reinforces the existing ground with tensile strength. In the process, nails are inserted into the soil in a closely spaced pattern to increase the overall shear strength of the earthen formation being treated. The nails are “passive” in that they are not pretensioned and develop tension as the ground deforms laterally in response to ongoing excavation. Most earthen retaining walls formed by the soil-nailing process are provided with temporary or permanent facing in the form of reinforced shotcrete. For permanent walls, a decorative facing is sometimes added.
As contrasted to more conventional reinforced soil retaining walls, soil-nail walls are constructed from the top down. Excavation occurs one layer at a time, from the top of the wall. As each layer is excavated, the nails are installed and facing is added. Successive layers are similarly constructed.
The soil-nails of the prior art comprise straight steel bars constructed of ductile steel and having a length of 60 to 100 percent of the height of the wall being constructed. Typical nails currently in use are categorized as follows:
Driven nails These nails are driven into place with a pneumatic or hydraulic hammer and may have an axial channel to permit the addition of grout sealing. They are generally small diameter (15-46 mm), with a relatively limited length up to about 20 m.
Grouted nails: These nails are inserted into preformed bore holes and then cement grouted. They may be ribbed to increase soil adhesion.
Jet grouted nails. These nails are installed using a high frequency Vibropercussion hammer, and cement grouting is injected during installation.
Launched nails. These nails are typically between 25 and 38 mm in diameter and up to 6 mm or longer and are fired directly into the soil with a compressed-air launcher.
As contrasted to the present invention, these prior soil-nails do not screw into place to directly grip and adhere to the soil continually and evenly over their entire length.